A device is known to detect a travel lane from an image of a road surface (Japanese Patent Unexamined Publication No. 2005-100000). The device disclosed in Japanese Unexamined Publication No. 2005-100000 generates a horizontal edge histogram for a plurality of edge points projected in reverse on coordinates of the road surface. The device then obtains peak positions in the edge histogram and makes the edge points contributing to the respective peak positions into a group, so as to detect lane markers.
When the vehicle changes lanes, the positions of the lane markers with respect to the vehicle are shifted from the positions before the lane change by the amount of lateral movement of the vehicle after the lane change. As a result, an edge group belonging to the common lane markers cannot be extracted correctly.